The present invention is directed, in general, to micro-electromechanical systems (MEMS) devices and, more specifically, to a drive circuit for a MEMS device and method of operating the same to drive a MEMS device.
Electrostatically actuated micro-electromechanical system (MEMS) devices have been proposed for a variety of applications. One promising use for MEMS devices is in optical switching and steering devices. In such devices, movable micro-machined mirrors are used as a switching element to direct an input optical signal to a desired output. The movement of the micro-machined mirrors is accomplished by electrostatic actuation.
In a typical MEMS device, an individual mirror is affixed to a movable support structure (i.e., a gimbal) via torsional elements such as springs. The gimbal may be coupled to a frame, also via torsional elements. Typically, two torsional elements positioned on opposing sides of the mirror, couple the mirror to the gimbal, and define an axis for mirror rotation. Similarly, two torsional elements positioned on opposing sides of the gimbal couple the gimbal to the frame, and define an axis for gimbal rotation.
In a typical situation, electrodes are positioned under the mirror and gimbal. The electrodes are configured to rotate the mirror or gimbal in either direction about its axis. The mirror or gimbal rotates under the electrostatic force between the mirror and gimbal, and is balanced in equilibrium by the restoring force of the torsional elements. The degree of rotation depends upon the amount of voltage applied to the electrodes. Traditionally, a degree of rotation up to about 9 degrees is achievable.
Prior-art attempts to drive the MEMS mirrors to a given degree of rotation used a digital to analog converter (DAC) and an amplifier, perhaps a high-voltage (HV) amplifier, to apply a voltage to each electrode for each axis. In order to control the mirror, a desired drive voltage was programmed into a first DAC to drive the HV amplifier, which in turn drove a first electrode of a given axis. A second DAC was programmed to zero volts, or ground, or virtual ground, and therefore a second electrode of a given axis was also driven to a zero drive voltage by the second DAC. However, the prior-art attempts required both a DAC and HV for each electrode, i.e, each axis used 2 DACs and 2 amplifiers, perhaps HV amplifiers. This plurality of components can lead to a loss of xe2x80x9creal estatexe2x80x9d on a chip, higher cost, undesirable thermal characteristics, and so on.
Accordingly, what is needed in the art is a drive circuit for a MEMS device and method of operating the same that overcomes the deficiencies of the prior art.
To address the above-discussed deficiencies of the prior art, the present invention provides a drive circuit for a MEMS device, an integrated circuit having a plurality of MEMS devices and drivers, a method of operating the drive circuit and a method of manufacturing the integrated circuit. In one embodiment, the drive circuit includes: (1) an electrode driver and (2) a switching network, coupled to an output of the electrode driver that: (a) in a first configuration, couples the output to a first electrode of an axis of the MEMS device and grounds an opposing second electrode of the axis of the MEMS device and (b) in a second configuration, couples the output to the second electrode and grounds the first electrode.
The present invention is based on the recognition that prior art MEMS device driver circuits employing two electrode drivers per axis essentially wasted one of the two driver circuits. While one driver circuit was performing the useful task of positioning the MEMS device, the other was producing nothing more than a ground signal to inactivate the opposing electrode. Since electrode drivers cost some amount of money to fabricate, occupy some space (xe2x80x9creal estatexe2x80x9d), require electricity to power and produce heat during operation, elimination of unnecessary electrode drivers is advantageous. The present invention therefore introduces a switching network that allows a single electrode driver to do the work that previously required two, and inactivates unused opposing electrodes to ground in a simpler and more direct manner.
In one embodiment of the present invention, the electrode driver includes: (1) a digital-to-analog converter and (2) an amplifier that provides the output. Those skilled in the pertinent art are familiar with the structure and function of conventional electrode drivers. The present invention can employ either conventional or later-discovered electrode drivers.
In one embodiment of the present invention, the first and second configurations are mutually exclusive. Alternatively, the first and second configurations may coexist, advantageously for only a brief period of time.
In one embodiment of the present invention, the switching network includes: (1) a first switch interposing the output and the first electrode, (2) a second switch interposing the output and the second electrode, (3) a third switch interposing the first electrode and an electrical ground and (4) a fourth switch interposing the second electrode and the electrical ground. In a more specific embodiment, the first and fourth switches operate in tandem, the second and third switches operate in tandem and the first and second switches are never simulaneously in an ON state. Of course, as stated above, the first and second switches may be simultaneously in an ON state, but advantageously for only a brief period of time.
In one embodiment of the present invention, the drive circuit further includes: (1) a second electrode driver and (2) a second switching network, coupled to an output of the second electrode driver that: (a) in a first configuration, couples the output to a third electrode of a second axis of the MEMS device and grounds an opposing fourth electrode of the second axis of the MEMS device and (b) in a second configuration, couples the output to the fourth electrode and grounds the third electrode. Therefore, the present invention can be extended to control multi-axis MEMS devices.
In one embodiment of the present invention, the electrode driver and the switching network are embodied in an integrated circuit. Those skilled in the pertinent art will understand, however, that the driver circuit of the present invention may be embodied in any appropriate conventional or later-discovered form.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.